Steam turbine

ABSTRACT

A steam turbine with at least one magnetic bearing for the shaft is provided, a metal paneling being attached in the area of a magnetic bearing. The metal paneling consists of metal rings insulated from one another. Further, cooling air ducts are provided in the area of the magnetic bearing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European Patent Office ApplicationNo. 08016914.7 EP filed Sep. 25, 2009, which is incorporated byreference herein in its entirety.

FIELD OF INVENTION

The present invention relates to a steam turbine with at least onemagnetic bearing for the shaft, with steel paneling being attached inthe area of a magnetic bearing.

SUMMARY OF INVENTION

A magnetic bearing represents an alternate option to the support methodsused to date. The outstanding attribute of the magnetic bearing is thelack of contact between supported part and bearing. The bearing forcesneeded are generated by an appropriate magnetic field which isestablished between the fixed part and the part to be supported. Thismeans that the magnetic bearing is friction-free and needs no lubricant.

If a magnetic bearing is used to support the shaft of a steam turbine,then the high temperatures occurring during the operation of the steamturbine are a problem for the magnetic bearing.

Metal paneling is attached in the area of the magnetic bearing tominimize the eddy current losses in the bearing. This metal panelingnormally consists of a number of metal rings insulated from one anotherby a suitable coating. The high temperatures in the shaft of a steamturbine can lead to the coating melting and thereby to the metalpaneling being destroyed.

An object of the present invention is thus to specify a steam turbinewith at least one magnetic bearing for the shaft with which overheatingof the magnetic bearing and thus destruction of the metal paneling isprevented.

This object is achieved for the steam turbine given above by air ductsrunning in the area of the magnetic bearing in a longitudinal directionof the shaft being embodied for a supply of cooling air, with the airducts being connected on the side of the magnetic bearing facing theblading to a cooling air supply device featuring a cooling air supplyrunning radially and ending at the free end of the shaft end in thebearing housing.

The explicit cooling of the magnetic bearing, specifically of a magneticbearing arranged at the hot end of a steam turbine, prevents overheatingof the insulating layers of the metal paneling and thereby destructionof the magnetic bearing.

Further expedient embodiments of the inventive steam turbine emerge fromthe dependent claims and from the subsequent description of variousexemplary embodiments of a steam turbine as claimed in the presentinvention which refer to the enclosed drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures show:

FIG. 1 part of a longitudinal section through a steam turbine accordingto the present invention,

FIG. 2 the detailed view D from FIG. 1,

FIG. 3 part of a longitudinal section through a magnetic bearing at ashaft end with the inventively provided cooling air duct, and

FIG. 4 part of a sectional perspective view of a shaft end withinventively provided cooling air ducts.

FIG. 5 part of a sectional perspective view of a shaft end with furtherinventively provided cooling air ducts.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows the modules of an inventive steam turbine needed tounderstand the invention. The steam turbine essentially consists of thefront bearing housing 1, the rear bearing housing 2 which is located atthe hot end of the steam turbine, and the center area 3 with theblading.

The shaft of the steam turbine is supported in the front bearing housing1 by a front screwed-on shaft end 4 and in the rear bearing housing 2 bya rear screwed-on shaft end 5.

FIG. 2 shows the section D through FIG. 1, i.e. FIG. 2 shows the rearbearing housing 2 in detail. The magnetic bearing 6 with the metalpaneling 7 is located in the rear bearing housing 2. Arranged below thelamination are cooling air ducts 9. The cooling air is supplied via acooling air supply duct 8 to these cooling air ducts 9 which arearranged in a helical structure underneath the magnetic bearing 6.

The individual cooling air ducts 9 end at the free end of the shaft endin the rear bearing housing 2.

FIG. 3 shows part of a longitudinal section through the rear bearinghousing 2 with the rear screwed-on shaft end 5. This figure shows twocooling air guides. One is the cooling air guide through the cooling airducts 9 which are arranged under the metal paneling 7 and end at thefree end of the rear screwed-on shaft end 5.

At the same time, in accordance with a development of the presentinvention, there is a further cooling air guide which is routed to theactual shaft 13 and is routed back from there through a central axialhole into the rear bearing housing 2. This cooling air guide is to bedescribed in greater detail below. The precise attachment of the shaftend 5 to the shaft 13 is not to be described in any greater detail here.The figure merely shows an insulation bearing housing disk 14 betweenthe actual shaft 13 and the screwed on shaft end 5. This insulating disk14 serves to interrupt the heat flow from the shaft 13 to the rearscrewed-on shaft end 5.

The cooling air supply 8 supplies both the cooling air ducts 9 and alsothe cooling air supply in the direction of the shaft 13. To this endradial blind holes 16 are provided at predetermined intervals in thearea of the cooling air supply 8 embodied in the shape of a ring.Starting from the end of the rear screwed-on shaft end 5 lying oppositethe actual shaft 13, a number of axial holes 18 are provided in theperiphery of the shaft end, which meet the radial blind hole 16. In thevicinity of the end of the screwed-on shaft end 5 adjacent to the actualshaft further radial blind holes 17 are provided, which meet theperipheral axial holes 18.

The axial holes 18 are each closed off at their start with a closurepiece 20. Furthermore a central axial hole 19 exists which leads throughthe entire screwed-on shaft end 5. In this way a further cooling airsupply is produced which leads, starting from the cooling air supply 8,through the radial blind holes 16, the peripheral axial holes 18, theradial blind holes 17, through a free space between a part of theperipheral surface of the screwed-on shaft end 5 and a part of the innerperipheral surface of the shaft 13, a chamber between shaft 13 andscrewed-on shaft end 5 and through the central axial hole 19.

This significantly reduces the heat transfer from the shaft 13 to therear screwed-on shaft end 5.

The cooling air guides for the rear screwed-on shaft end are describedhere. Naturally identical cooling air guides are possible for the frontscrewed-on shaft end.

Also with the two shaft ends, when the circumstances allow, the secondcooling air guide can be dispensed with.

FIG. 4 shows part of a perspective cross sectional view of a shaft endwith cooling air ducts 9 provided in accordance with the invention. Thecooling air ducts 9 are led radially outwards by means of a ring 12consisting of 2 parts in order to have cooling air applied to them bymeans of the cooling air supply 8. The cooling air ducts 9 are formed bycorresponding grooves in the shaft end as well as by the metal paneling7 of the magnetic bearing.

FIG. 5 shows part of a cross-sectional perspective view of a shaft endwith further cooling air ducts 25 and 26 provided in accordance with theinvention. These air ducts are formed either by grooves 25 on the innerside of the collar 22 carrying the metal paneling 23 or by axial holes26 in the collar 22. The cooling air ducts are led radially outwards bymeans of a ring 24.

1-5. (canceled)
 6. A steam turbine, comprising: a magnetic bearing for ashaft of the steam turbine; a metal paneling being attached in an areaof the magnetic bearing; cooling air ducts running in a longitudinaldirection of the shaft in the area of the magnetic bearing for coolingair to be supplied; and a cooling air supply device, the cooling airducts being connected on a side of the magnetic bearing facing towardsthe blading to the cooling air supply device, wherein the cooling airsupply device includes a cooling air supply running radially and endingat a free end of the shaft end in a bearing housing of the magneticbearing.
 7. The steam turbine as claimed in claim 6, wherein the shaftincludes grooves running axially in the area in which the metal panelingis attached, the grooves forming the cooling air ducts along with themetal paneling of the shaft.
 8. The steam turbine as claimed in claim 6,further comprising: collars, the collars being attached to the shaft inthe area of the magnetic bearing and carrying the metal paneling,wherein inner sides of the collars include grooves which form thecooling air ducts together with the shaft surface.
 9. The steam turbineas claimed in claim 6, further comprising: collars, the collars beingattached to the shaft in the area of the magnetic bearing and carryingthe metal paneling, wherein holes in the collars form the cooling airducts.
 10. The steam turbine as claimed in claim 6, wherein the shaft isdivided into three parts and consists of a central piece carrying theblading and two screwed-on shaft ends, and wherein further cooling airducts branch off from the cooling air supply duct, the further coolingair ducts leading via radial and axial holes in the peripheral area of ashaft end to an end of the screwed-on shaft end adjoining the centralpiece of the shaft, a chamber between the end of the shaft and thescrewed-on shaft end being embodied, the further cooling air ductsleading from the chamber via a central axial hole to a free end of thescrewed-on shaft end.
 11. The steam turbine as claimed in claim 7,wherein the shaft is divided into three parts and consists of a centralpiece carrying the blading and two screwed-on shaft ends, and whereinfurther cooling air ducts branch off from the cooling air supply duct,the further cooling air ducts leading via radial and axial holes in theperipheral area of a shaft end to an end of the screwed-on shaft endadjoining the central piece of the shaft, a chamber between the end ofthe shaft and the screwed-on shaft end being embodied, the furthercooling air ducts leading from the chamber via a central axial hole to afree end of the screwed-on shaft end.
 12. The steam turbine as claimedin claim 8, wherein the shaft is divided into three parts and consistsof a central piece carrying the blading and two screwed-on shaft ends,and wherein further cooling air ducts branch off from the cooling airsupply duct, the further cooling air ducts leading via radial and axialholes in the peripheral area of a shaft end to an end of the screwed-onshaft end adjoining the central piece of the shaft, a chamber betweenthe end of the shaft and the screwed-on shaft end being embodied, thefurther cooling air ducts leading from the chamber via a central axialhole to a free end of the screwed-on shaft end.
 13. The steam turbine asclaimed in claim 9, wherein the shaft is divided into three parts andconsists of a central piece carrying the blading and two screwed-onshaft ends, and wherein further cooling air ducts branch off from thecooling air supply duct, the further cooling air ducts leading viaradial and axial holes in the peripheral area of a shaft end to an endof the screwed-on shaft end adjoining the central piece of the shaft, achamber between the end of the shaft and the screwed-on shaft end beingembodied, the further cooling air ducts leading from the chamber via acentral axial hole to a free end of the screwed-on shaft end.